Batteries have a property to release the stored energy in small amounts (this phenomenon is called ‘self-discharge’). This property is particularly noticeable in rechargeable batteries such as Nickel Metal Hydride Batteries etc. as compared to dry cell batteries, hence disabling rechargeable batteries from becoming batteries that ‘customers can use immediately after purchase’. For this reason, rechargeable batteries couldn’t be used unless charged after purchase and so lagged behind dry cells in convenience. This new product’s main property is that it has introduced great improvements in self-discharge properties (residual ratio after one year of non use is 85%*4, in temperature conditions of 20 degree Celsius according to SANYO research). Through this breakthrough development, SANYO has realized a rechargeable battery that can challenge dry cell batteries in user-friendliness through features such as making possible use immediately after purchase or once charged, its ability to be used anytime.

Low self-discharge - the key-advantage

The key-advantage of the eneloop compared to usual rechargeable batteries is its extremely low self-discharge.

Retains Capacity... Even After 12 Months

Once charged, eneloop retains its charged capacity even after 6 or 12 months of storage
(90% of Charged Capacity retained after 6 months, 85% Capacity after 12 months).

eneloop batteries are pre charged and is ready for immediate use after purchase, straight from the pack. Just like Primary Batteries. There is no need to charge-before-use.

Comparison of remaining capacity over time

Once charged, eneloop keeps its charge even if you store it for 6 or 12 months.

( 90 per cent of the charge after 6 months, 85 per cent after 12 months )

For a rechargeable battery this is a revolutionary advantage.

No more worries about the state of charge of your battery.

Just, charge them and keep them.

Even after months you will still have an almost fully charged battery.

In contrast to a disposable battery the eneloop can be charged 1000 times. This saves the environment and your purse.

Thus one eneloop saves the waste of 999 disposable batteries.

How was the self-discharge reduced?

Modern Ni-MH batteries consist of two metal stripes ( anode and cathode ),  which are separated by a non-conductive porous plastic foil ( separator ).

These three stripes are laid on top of each other and are winded to a coil.

This coil is put in a metal can and immersed with a liquid ( electrolyte ). 

Then the metal can is closed with a cap. 

The self discharge of Ni-MH batteries is caused by three main reasons: 

Now, how could the self-discharge in the eneloop been reduced?

The chemical decomposition of the cathode has been reduced substantially by the use of a new super lattice alloy.

As an additional benefit the super lattice alloy increases the electrical capacity of the battery and reduces the internal resistance, which allows higher discharge currents. 

Another advantage of the reduced decomposition of this alloy is the fact, that less Cobalt is needed to stabilize the alloy.

The anode has been strengthened by another new material, which reduces the natural disaggregation. 

Additionally the separator and the used electrolyte have been optimized for low self discharge of the eneloop

SANYO has been a market leader in nickel metal hydride batteries for the consumer market. The synergy of the following proprietary technologies of SANYO in developing high capacity products has made the successful development of ‘eneloop’ possible:

These are a few of the technologies that have helped contain self-discharge during the period for which the battery is not in use. Furthermore, it also inhibits voltage reduction even after a long period of being out of use.